This invention relates generally to labyrinth seals in turbo machinery or the like. More particularly, but not by way of limitation, this invention relates to improved labyrinth seals which reduce or eliminate the inlet swirl and/or circumferential flow of fluid within the labyrinth seals thereby reducing the destabilizing influence of labyrinth seals which can induce rotor instability.
Although this invention is applicable to numerous and various types of labyrinth seals, it has been found to be particularly useful in the environment of impeller covers and balance pistons or rotating elements of compressors. Therefore, without limiting the applicability of the invention to "labyrinth seals for impeller covers and balance pistons or rotating elements in compressors", the invention will be described in such environments.
The destabilizing influence of labyrinth seals is a major source of excitation leading to rotor instability in turbo machinery. The magnitude of this excitation is a function of the circumferential flow of fluid within the labyrinth seal and can be greatly reduced by eliminating or greatly reducing the inlet swirl associated with the labyrinth seal.
Studies have been done which indicate that in long labyrinth seals, fluids with zero inlet swirls can acquire a significant tangential velocity component as it traverses along the length of the labyrinth seal. The tangential velocity component is caused by the viscous drag effects from the rotating shaft or rotating element.
Attempts have been made, with some success, to reduce or eliminate the inlet swirl associated with division wall labyrinths in high pressure barrel compressors through the use of shunt holes which introduces fluid from a region of high pressure into a region within the seal cavity. This concept has not been used in other labyrinths partly because of the complex drilling required in the diaphragms, volutes, housings, etc.
The present invention provides an improved labyrinth seal which reduces or eliminates the inlet swirl and the tangential velocity component as the fluid traverses the labyrinth seal by the use of a plurality of bypass passageways in the labyrinth seal positioned at specific locations in the seal to provide an alternate flow path for the fluid.